NASA urges people not to go near debris from Columbia because it could contain toxic substances. People who find debris are asked to call (281) 483-3388. NASA has also set up a Web site to collect information that may be helpful in the investigation of the shuttle disaster.

JOHNSON SPACE CENTER, Texas (CNN) --Federal investigators arrived in Texas and Louisiana on Sunday and formed teams to undertake the massive task of determining what went wrong when the space shuttle Columbia broke apart Saturday morning.

A series of teams with different tasks -- some formed to find debris, others created to assess data compiled during Columbia's final moments -- fanned out Sunday afternoon, said Ron Dittemore, NASA's top shuttle program manager. They will report to the Columbia Accident Investigation Board, based at Barksdale Air Force Base in Shreveport, Louisiana.

"We're becoming very organized and making progress in support of each other," Dittemore said at a news conference at the Johnson Space Center, near Houston, Texas.

Investigators have determined that something happened to make the temperature on Columbia's left side increase significantly faster than temperatures on its right side, Dittemore said. In five minutes, he said, monitoring devices showed that the temperature on Columbia's mid-fuselage increased by 60 degrees, while the right side recorded a spike of 15 degrees.

Just before the shuttle broke apart, he said, the drag on its left side was so pronounced that the vessel's right ailerons tried to correct the drag to keep Columbia on an even keel.

"Soon after, we had loss of signal," Dittemore said.

Also Sunday, investigators turned their attention to Lockheed Martin's Michoud Assembly Facility in New Orleans, Louisiana, where the shuttle's external fuel tank was built. A piece of foam fell off the 154-foot tank during launch January 16, striking heat-resistant tiles on the shuttle's left wing, NASA officials said.

After extensive analysis, NASA officials determined that the mishap did not present a safety concern for the shuttle, but in light of Columbia's disintegration at 200,000 feet, chief flight director Milt Heflin said, investigators would take a closer look at the incident.

NASA has suspended all shuttle flights pending the outcome of the investigation, which will include a review by an independent board led by retired Navy Adm. Harold Gehman, who headed the probe of the attack on the USS Cole in October 2000 in Yemen.

"We're going to provide all the information in our internal investigation and let the facts speak to what happened," NASA Administrator Sean O'Keefe said Sunday. "And we're going to correct it and move on and be sure that we fly safely, as is our commitment, each and every time we launch and each and every time there's a landing."

NASA officials said readings were lost for the left-wing hydraulic sensors and left-side landing gear tire pressure, and that the shuttle experienced intense heat before it broke up Saturday morning.

Tiles, stress studied

Questions arose Sunday about Columbia's tiles, which were designed to protect the shuttle from the intense heat of atmospheric re-entry.

Speculation also shifted to whether aerodynamic stress could have affected the 90-ton shuttle, which has been likened to a flying brick with wings as it plunges from orbit into the atmosphere, controlled not by engines but aerial flaps.

Should a shuttle steer in the wrong direction as it re-enters the atmosphere, going at many times the speed of sound, it could fly out of control and break apart because of the extreme stress, according to science experts.

Federal officials ruled out the possibility of terrorism, given the shuttle's altitude when it broke apart.

The last communication Johnson Space Center had with the Columbia crew before the spacecraft disintegrated referred to tire pressure.

Mission Control: "And Columbia, Houston, we see your tire pressure messages, and we did not copy your last."

Crew member: "Roger." [indiscernible]

After the shuttle Challenger exploded 17 years ago, the shuttle fleet was grounded for two years as NASA investigated the mishap.